The present invention relates generally to electronic devices, integrated circuit components and interface materials used in assembling such components. More specifically, the present invention relates to gasket and interface materials used in assembling these devices that also function for transferring the heat generated within such devices and providing shielding against the effects of electro-magnetic interference (EMI).
In the small electronics and computer industries, it has been well known to employ various types of electronic component packages and integrated circuit chips, such as the central processing chips employed within cellular telephones and the central processing units (CPU""s) used within palmtop computers like the Cassiopeia manufactured by Casio. These integrated circuit chips have a pin grid array (PGA) package and are typically installed into a socket, or are soldered directly onto a computer circuit board. These integrated circuit devices, particularly the CPU microprocessor chips, generate a great deal of heat during operation which must be removed to prevent adverse effects on operation of the system into which the device is installed. For example, the CPU within the Cassiopeia, a microprocessor containing millions of transistors, is highly susceptible to overheating which could destroy the microprocessor device itself or other components proximal to the microprocessor.
In addition to the Cassiopeia microprocessor discussed above, there are many other types of semiconductor device packages that are commonly used in other types of small electronics. Recently, various types of surface mount packages, such as BGA (ball grid array) and LGA (land grid array) type semiconductor packages have become increasingly popular as the semiconductor package of choice for small electronics.
The aforementioned electronic components are commonly employed in electronic devices, such as computers and cellular phones. These devices are being manufactured smaller and smaller and include faster and faster electronic components therein. As a result, heat generation and overheating continues to be a serious concern while the sizes of the devices get smaller. Therefore, problems arise as to how to effectively cool the small electronic components within the small and cramped environments within the device. Typical cooling solutions such as heat sinks and fans are not preferred because they are large and, as a result, consume large spaces within an already cramped electronic device case. In addition, since these small devices, such as cellular phones or laptop computers, must balance competing demands for higher power requirements, smaller battery sizes with the associated power limitations and overall device case size, active cooling solutions, such as powered fans and the like, are not desirable.
In addition, electromagnetic interference shielding is often required to ensure proper operation of the electronic device. Typically the shielding takes the form of a shielding layer within the device case, which encases the electronic component within the device to be protected. In these instances, a gasket must also be employed between the case components to prevent EMI form entering the device at the seam between the components. For example, in a cellular phone, there is typically a top housing and a bottom that mate to one another. A gasket is provided at the junction between the top housing and the bottom housing to prevent EMI from entering the device therebetween.
These gaskets are well known in the present art and are typically made of metal, such as aluminum, and are cast or machined into the desired configuration. Such manufacturing techniques are expensive and cumbersome, particular where the gasket includes complex geometries. In addition, metallic parts are relatively heavy, creating another drawback to their use. Alternatively, the gaskets may be manufactured of plastic or rubber, such as by injection molding, which is a relatively inexpensive process and provides a lightweight solution. However, such plastic or rubber material is inadequate for providing heat dissipation or heat transfer between the case components and is ineffective as EMI shielding. A plastic gasket may be plated to provide EMI shielding and thermal conductivity, but plating provides inferior thermal conductivity.
Therefore, in view of the foregoing, inexpensive lightweight injection molded gaskets that can be easily and cheaply manufactured yet still provide EMI shielding are highly desired. Gaskets that are also highly thermally conductive are further desired to assist in heat transfer between the outer case components of the device and the dissipation of heat from the electronic components within the device, such as microprocessor chips. There is also a demand for a gasket for use in an electronic device that is lightweight, has a low profile and is net-shape moldable from a thermally conductive material so that complex geometries for accurate mating of the case surfaces can be achieved.
The present invention is generally directed to a novel and unique gasket material for use in electronic device construction, providing a sealed construction that includes an improved heat dissipating system for cooling heat generating devices and provides shielding against the infiltration of electromagnetic interference (EMI) or radio frequency waves. The elastomeric gasket of the present invention enables complex shapes to be injection molded cost-effectively while providing passive cooling and improved EMI shielding for the electronic components contained within the device into which the gasket is incorporated.
In accordance with the present invention, an elastomeric gasket for providing a seal between the mating surfaces of the case sections of an electronic device is provided. The electronic device includes an electronic circuit board with a heat generating electronic component installed thereon, and at least two separate outer case components between which the gasket of the present invention is installed. The heat generating components on the circuit board are installed in such a manner as to be in thermal communication with one of the outer case components and may also be in thermal communication with the gasket of the present invention. In this configuration, the heat generated within the device can be transferred through one of the outer case components or through the gasket of the present invention to the other case components to provide increased surface area for improved heat dissipation. In addition, since the gasket of the present invention is elastomeric, it is inherently compressible, providing an effective seal between the gaps in the outer case components.
The elastomeric gasket is injected molded from a net shape moldable thermally conductive polymer composition. As the elastomeric gasket of the present invention is fabricated from plastic materials it is lighter than the metallic materials previously employed. In addition, the present invention also has the advantage of being net shape moldable, meaning, the part that is created in the injection molding process does not require any further processing steps after it is removed from the mold and before it is incorporated into the finished device. Both the lighter weight and the net-shape moldability are distinct advantages over the prior art where metallic parts had to be machined in several steps to achieve the desired part geometry.
Another feature of the present invention is the electromagnetic interference (EMI) shielding provided. Normally a separate EMI shield is installed in an electronic device. The shield acts as a shroud around the electronic component to shield it from electromagnetic interference. However, such a shield effectively encases the electronic component making access thereto for dissipating heat very difficult, if not impossible. Further, the EMI shield encasement prevents airflow to the electronic component for cooling. Since the gasket of the present invention is constructed from thermally conductive polymers it inherently absorbs EMI waves and prevents their leakage through the seam of the case components thereby preventing transmission to the electronic circuitry inside the device without the installation of an additional component. This feature is particularly important in applications such as cellular telephones where EMI waves can prevent the device from functioning properly. Thus a thermally conductive elastomeric gasket employed with a thermally conductive device case can effectively dissipate the heat generated within the device while assisting in shielding the electronic components from EMI waves without the addition of a separate EMI shield part that could potentially interfere with the heat transfer from the device.
It is therefore an object of the present invention to provide an elastomeric gasket for use in an electronic device that enhances the dissipation of heat from a heat generating electronic component mounted therein.
It is also an object of the present invention to provide an elastomeric gasket for use in an electronic device that directly provides heat dissipation for a heat generating electronic component mounted therein.
It is a further object of the present invention to provide an elastomeric gasket for use between the components of an electronic device case that passively provides heat transfer between the case components while sealing the gap therebetween.
Another object of the present invention is to provide an elastomeric gasket for use an electronic device that simultaneously seals the case components against the leakage of electromagnetic interference and provides heat transfer between the components of the device.
It is a further object of the present invention to provide an elastomeric gasket for an electronic device that is injection moldable from a thermal composite material into complex geometries to accommodate a variety of device case shapes.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.